Restore missing initialization of text thread actions (#33422)

Fixes a regression introduced in
https://github.com/zed-industries/zed/pull/33289

Release Notes:

- Fixed a bug where some text thread actions were accidentally removed.

crates/agent_ui/src/agent_ui.rs

@@ -48,7 +48,7 @@ pub use crate::agent_panel::{AgentPanel, ConcreteAssistantPanelDelegate};
 pub use crate::inline_assistant::InlineAssistant;
 use crate::slash_command_settings::SlashCommandSettings;
 pub use agent_diff::{AgentDiffPane, AgentDiffToolbar};
-pub use text_thread_editor::AgentPanelDelegate;
+pub use text_thread_editor::{AgentPanelDelegate, TextThreadEditor};
 pub use ui::preview::{all_agent_previews, get_agent_preview};
 
 actions!(
@@ -157,6 +157,7 @@ pub fn init(
     agent::init(cx);
     agent_panel::init(cx);
     context_server_configuration::init(language_registry.clone(), fs.clone(), cx);
+    TextThreadEditor::init(cx);
 
     register_slash_commands(cx);
     inline_assistant::init(